In the case of a scroll gas compressor provided with low-vibration and low-noise characteristics, a suction chamber is present at the outer boundary of a swirl for forming a compressed space and the discharge port is provided for the center of the swirl. Moreover, the scroll gas compressor has a characteristic that the compression ratio is constant so that the volume ratio determined between the volume at completion of suction and the volume at completion of compression becomes constant.
Therefore, when the suction pressure and the discharge pressure are almost constant, a high efficiency can be realized by optimizing a set compression ratio.
When variable-speed motion is performed or air-conditioning load fluctuates by using the scroll gas compressor as a refrigerant compressor for air conditioning, the suction pressure and discharge pressure of the refrigerant are changed. Then, insufficient compression or excessive compression occurs due to the difference between actual compression ratio and set compression ratio.
In the case of insufficient compression, the high-pressure refrigerant gas in a discharge chamber intermittently flows backward from a discharge port to a compression chamber to cause the input to increase. In the case of excessive compression, compression power more than necessary power is required. As means for reducing excessive compression, it is known to form a bypass hole. A scroll gas compressor provided with the above bypass hole is disclosed in JP B8-30471.
To optimize the efficiency by the scroll gas compressor provided with the bypass hole as described above, it is necessary that the bypass hole makes the compression chamber communicate with the discharge chamber at an equal compression ratio in a pair of symmetric compressed spaces formed by the engagement between fixed and revolving scrolls.
For example, when manufacturing a fixed scroll with a casting and a revolving scroll with an aluminum alloy, a difference may be observed between scroll wrap shapes due to a difference between thermal expansion coefficients because the temperature of a scroll wrap portion rises during operation. When this phenomenon occurs, the gap between scroll wraps during operation changes, a difference occurs between leak gaps under the compression process, and a difference is observed between pressure rises under the compression process also in a pair of symmetric compressed spaces. Bypass holes are symmetrically arranged in general. When symmetrically arranging the bypass holes, however, the bypass holes communicate with each other at a point where a compression ratio differs in a pair of compressed spaces. To optimize the efficiency, it is necessary to make bypasses communicate with each other at an equal compression rate in a pair of symmetric compressed spaces.
Also in the case of a structure in which a spiral sealing member is set to the front end of a revolving scroll, a difference may be observed between compression rises under the compression process in a pair of symmetric compressed spaces. Therefore, the same consideration is necessary.
JP B8-30471 discloses the position of a bypass hole to optimize the efficiency but the positional relation between bypass holes in a pair of symmetric compressed spaces is not specified.
It is conventional to form a fixed scroll of a cast material to improve its durability, and to form a revolving scroll of an aluminum alloy to reduce its centrifugal force. However, there is a substantial difference in thermal expansion coefficient between a cast material and an aluminum alloy. Therefore, the wrap form differs from the revolving scroll to the fixed scroll, when they are operated and thus heated. As shown in FIG. 4, the compression chambers differ from each other in the degree of sealing effect. In the conventional devices, the bypass holes do not function optimally under such conditions. The main object of the present invention is, therefore, to solve these problems by providing asymmetrical arrangement of the bypass holes.